how to specify instruction size for optimization

[cirrus75]

  Hi,

I could not understand exactly how to specify instruction size to gcc (so it can really optimize the code size when -Os is used).

I would like to inform gcc that if some registers are used for certain operations, the instruction will be smaller. For example, an add which destination register is register 4 has lowest size if compared to all "add" forms.

What is the easiest way to give this information to gcc ? I took a long look at the internals documentation and other ports but I'm not sure.

thank you for the help,

Alex Prado